In the past, in an access network for connecting a station and a user home, a PON system, which is one type of an FTTH (Fiber To The Home), rapidly spreads because high speed and economy can be attained. In the PON system, a plurality of subscriber side apparatuses (ONUs: Optical Network Units) are connected to a station side apparatus (OLT: Optical Line Termination) via an optical splitter that diverts a signal output to a plurality of optical fibers. TE (Terminal Equipment) is connected to the ONUs via a LAN cable. The TE is, for example, an HGW (Home Gate Way), a VoIP-TA (Voice over Internet Protocol-Terminal Adapter), a PC, or the like.
The ONU set in the user home needs to always establish, to provide a service requiring real time property such as an optical telephone, a link to the OLT and the TE even when data communication is not performed (during standby). There is a problem in that power consumption of the ONU is large.
To solve the problem, Patent Literature 1 described below discloses a method in which, in each-call control of a PDS (passive double start) configuration, a specific pattern is set for each terminal line terminating apparatus and, in incoming call, the terminal line terminating apparatus compares a specific pattern transmitted from an intra-office line terminating apparatus and the set (registered) pattern in the terminal line terminating apparatus and performs, only when the patterns coincide with each other, an incoming operation to suppress unnecessary power consumption.
Patent Literature 2 described below discloses a method of suppressing unnecessary power consumption by stopping, when there is no exchange of valid data between a modem and a line card in an ATM (Asynchronous Transfer Mode) apparatus, functions of the modem and a transmitting unit of the line card.
Patent Literature 3 discloses a method of monitoring states of a logical link and a physical link in an ONU of a PON system and controlling a mounted circuit in the ONU to a low power consumption mode in a state in which the links are disconnected.
Patent Literature 1: Japanese Patent Application Laid-open No. H09-64903
Patent Literature 2: Japanese Patent Application Laid-open No. 2004-64458
Patent Literature 3: Japanese Patent Application Laid-open No. 2008-113193